2. The Mysticeti, which are the baleen whales, such as humpback whales, blue whales, right whales, etc.

So, even though the sperm whale, and the killer whale and beluga whale, etc. are all whales, they are closer to dolphins than to the baleen whales in the phylogenetic tree. Thus, the term 'whale' is not that important, because basically it means a medium to large size cetacean.

Incidentally, beluga whales and narwhals are closely related and are the only members of the family Monodontidae